Compositions and methods for platelet enriched fibrin constructs

ABSTRACT

Compositions and methods are provided for tissue constructs that promote wound healing. The composition comprises a dimensionally stable fibrin construct for local administration to a wound site or region. In one embodiment, the fibrin construct is a wound healing composition, including components that promote wound healing, such as platelets, growth factors, white blood cells and fibrin clots. In another embodiment, the tissue treatment composition includes (i) aggregated fibrin, (ii) blood cells, and (iii) optionally, growth factors and/or other proteins.

FIELD OF THE INVENTION

The present invention relates generally to compositions and methods ofplatelet enriched fibrin contructs for delivery.

BACKGROUND OF THE INVENTION

Wound healing, or wound repair, is an intricate process in which theskin (or another organ-tissue) repairs itself after injury. In normalskin, the epidermis and dermis exists in a steady-state equilibrium,forming a protective barrier against the external environment. Once theprotective barrier is broken, the normal (physiologic) process of woundhealing is immediately set in motion. The classic model of wound healingis divided into three or four sequential, yet overlapping phases: (1)hemostasis, (2) inflammatory, (3) proliferative and (4) remodeling. Uponinjury to the skin, a set of complex biochemical events takes place in aclosely orchestrated cascade to repair the damage. Within minutespost-injury, platelets (thrombocytes) aggregate at the injury site toform a fibrin clot. This clot acts to control active hemostasis.

Fibrin clots act as a hemostatic barrier to reduce the risk of serum,lymph and liquid leakage and are frequently used to reduce blood lossduring/after surgery. The fibrin sealants, formed by mixing aconcentrated solution of fibrinogen with thrombin and calcium ions toproduce fibrin, are impractical because the prepartion method requiresseveral hours and results in a crude clotting factor concentrate that isuseful to manage hemostatically-deficient patients, but is not practicalfor harvesting fibrinogen from small volumes of blood.

Fibrin glues are well-known in the art for use in hemostasis, tissuesealing and wound healing, and have been commercially available outsidethe United States for more than a decade. Fibrin glues mimic the laststep of the coagulation cascade and are usually commercialized as kitscomprising components to form a three-dimensional network commonlycalled “Fibrin Gel.” However, an important and well known disadvantageof the known fibrin glue preparations resides in the water-like fluidityof the components, which leads to considerable handling difficulties ofthe glues. Efforts have been made to overcome this problem andfacilitate the mixing of the components by the development of particularapplication modes such as a double-syringe applicator (e.g. thatsupplied under the trade name Duploject®, Immuno AG, Vienna, Austria,and which is disclosed in e.g. U.S. Pat. No. 4,359,049, or a specialspray system as disclosed in e.g. EP-A-156 098). The basic problem witha low viscosity glue still remains.

Multiple problems exist with the present tissue sealants. First, anon-viscous or low viscosity glue is unsuitable for use onnon-horizontal surfaces since it will run off before setting. Second,there is a definite risk of a non-viscous or low vicosity glue runningoff to sites where it is unwanted and where it might causecomplications. This is particularly the case in vascular surgery sincethe fluid glue may reach inside the vessels before it sets and therebycause thromboembolic complications. An instantaneously setting fibringlue (containing a high concentration of thrombin), on the other hand,cannot be used where the parts to be sealed require subsequentadaptation.

Moreover, the present solutions do little to expedite wound healing.Recombinant or xenogenic growth factors can be targeted for delivery toa desired site within a subject to speed and the healing process.However, delivery vehicles for growth factors are not always reliable orable to remain in the desired location for a sufficent period of time.Moreover, formulation and delivery of multiple growth factors, which areoften needed for improved healing, are not practical due to cost andavailability.

Therefore, a need remains for improved methods and compositions forwound healing, and specifically for methods and compositions to delivermultiple growth factors to a site for tissue healing and/or repair.

SUMMARY OF THE INVENTION

The present invention generally provides compositions and methods forpreparing a wound healing construct. One aspect discloses a method ofpreparing a growth factor enriched construct including the steps ofcollecting a blood sample, mixing the blood sample in a container,exposing the blood mixture to a separation force and harvesting adimensionally stable, suturable fibrin construct. Another aspectdiscloses a bioimplantable construct including a fibrin construct havinga growth factor enriched surface and a growth factor depleted surface,where the fibrin construct is dimensionally stable and suturable. Anadditional aspect discloses method of regenerating, repairing oraugmenting damaged or injured tissue in a subject by obtaining a fibrinconstruct and delivering the fibrin construct to a target site. Yetanother aspect discloses a kit including a borosilicate container, ananti-coagulant, a coagulation activator, and a cross-linking agent.

One aspect includes a method of preparing a growth factor enrichedconstruct by collecting a blood sample comprising unaggregated fibrin inthe presence of an anti-coagulant, mixing the blood sample in acontainer with a coagulation activator to initiate aggregation of thefibrin, exposing the blood mixture to a separation force that separatesthe blood mixture into a gradient of plasma, aggregated fibrin and bloodcells, and harvesting the aggregated fibrin and at least a portion ofthe blood cells to form a dimensionally stable, suturable fibrinconstruct, wherein the fibrin construct has a growth factor enrichedsurface concentrated with white blood cells and platelets capable ofreleasing a growth factor and an opposed, growth factor depletedsurface. The growth factor depleted surface can be substantially lackingin blood cells. The growth factor depleted surface can be substantiallylacking in red blood cells.

In one embodiment, the method includes the fibrin construct havingparticular physical properties to be dimensionally stable. The physicalproperties can include durability under stress and resiliency. In anexemplary embodiment, the fibrin construct can have a resiliency that ismeasured by an elongation at break strength of at least 200%. In anotherexemplary embodiment, the fibrin construct can have a strength that ismeasured by an ultimate strength of at least 0.15 MPa. In yet anotherexemplary embodiment, the fibrin construct can have a strength that ismeasured by a compression strength of at least 30 kPa.

In another embodiment, the method can include the fibrin constructhaving blood cells, such as can include platelets, white blood cells,and/or red blood cells, where the platelets can further includeunactivated and activated platelets. In an exemplary embodiment, theblood cells include white blood cells and platelets.

In yet another embodiment, the method can include obtaining the bloodsample from a single donor or from multiple donors mixed together toobtain a single blood sample. The blood sample can further be obtainedfrom the same subject who will receive the fibrin construct.

Thus, the blood is autologous to the recipient. The blood sample canalso be obtained from a non-autologous subject or donor or multipledonors. Moreover, the blood sample can be obtained from a heterologoussubject or donor or multiple donors. Thus, the blood sample can beobtained from one or more subjects. In an exemplary embodiment, theblood sample can be obtained from a single donor or from multipledonors.

In one more embodiment, the method can include mixing the blood samplein a container, such as glass. The container can be a borosilicate glasscontainer.

The blood sample can also be mixed with one or more coagulationactivators or clotting factors to induce coagulation. In a particularembodiment, the coagulation activator can be calcium chloride.

The blood sample can also be exposed to one or more separation forces,such as centrifugation. In an exemplary embodiment, the separation forceincludes more than one centrifugations. The first centrifugation can beat a speed of at least 2000 xg and an optional second centrifugation canbe at a speed of at least 2000 xg. In an additional embodiment, theseparation force includes a single centrifugation at a force of at least2000 xg, but preferably at least 3000 xg.

The method can also include modifying the fibrin construct afterharvest. Such modifications can include removing excess liquid from thefibrin construct by blotting the fibrin construct on an absorbentmaterial; folding the fibrin construct upon itself to form a foldedconstruct such that adjacent halves of the growth factor enrichedsurface contact each other and form an inner portion of the foldedconstruct while growth factor depleted surface forms an outer portion ofthe folded construct; forming a multilayered construct by layering asecond fibrin construct on top of the first fibrin construct such thatthe growth factor enriched surfaces of each construct are in contactwith each other and the growth factor depletedsurfaces of each of theconstructs form outer surfaces of the multilayered construct; andcross-linking the fibrin construct.

Another aspect discloses an bioimplantable construct including a fibrinconstruct derived from whole blood, having a growth factor enrichedsurface concentrated with blood cells and platelets capable of releasinga growth factor and a growth factor depleted surface, the fibrinconstruct being dimensionally stable and suturable. The growth factordepleted surface can also be substantially lacking in blood cells, suchas red blood cells, white blood cells, platelets. The growth factordepleted surface can be substantially lacking in red blood cells. Inanother embodiment, the growth factor depleted surface can include whiteblood cells.

The fibrin construct can have particular physical properties thatfurther define its dimensional stability. The physical properties caninclude durability under stress and resiliency. In an exemplaryembodiment, the fibrin construct can have a resiliency that is measuredby an elongation at break strength of at least about 200%. In anotherexemplary embodiment, the fibrin construct can have a strength that ismeasured by an ultimate strength of at least about 0.15 MPa. In yetanother exemplary embodiment, the fibrin construct can have a strengththat is measured by a compression strength of at least about 30 kPa.

The fibrin construct can also be modified. Such modifications canprotect one or more sides of the fibrin construct. In an exemplaryembodiment, the fibrin construct is a folded construct that is foldedupon itself so that adjacent halves of the growth factor enriched layercontact each other and form an inner portion of the folded constructwhile the growth factor depletedsurface forms an outer portion of thefolded construct. The fibrin construct can further be sutured along atleast one edge thereof to secure the folded construct in the foldedcondition.

The fibrin construct can also be in the form of a multilayered constructin which two fibrin constructs are joined together with the growthfactor enriched surfaces facing each other forming an inner portion ofthe multilayered construct and the growth factor depletedsurfacesforming an outer portion of the multilayered construct. Like the foldedconstruct, the multilayered construct can also include sutures extendingbetween the adjacent constructs along at least a portion of an edgethereof to secure the multilayered construct

An additional aspect includes a method of regenerating, repairing oraugmenting damaged or injured tissue in a subject by obtaining a fibrinconstruct as disclosed and delivering the fibrin construct to a targetsite in the subject to regenerate, repair or augment damaged or injuredtissue.

In one embodiment, the method can include obtaining the blood samplefrom a single donor or from multiple donors mixed together to obtain asingle blood sample. The blood sample can further be obtained from thesame subject who will receive the fibrin construct. Thus, the blood isautologous to the recipient. The blood sample can also be obtained froma non-autologous subject or donor or multiple donors. Moreover, theblood sample can be obtained from a heterologous subject or donor ormultiple donors. Thus, the blood sample can be obtained from one or moresubjects. In an exemplary embodiment, the blood sample can be obtainedfrom a single donor or from multiple donors.

In another embodiment, the method can include delivering the one ormultiple fibrin constructs to a target site. Multiple fibrin constructscan be joined together prior to delivery to the target site, such as bysuturing and/or gluing the fibrin constructs together. One or morefibrin constructs can also be shaped to correspond to the target site.Shaping the fibrin constructs can include joining multiple fibrinconstructs, such as by suturing and gluing the fibrin constructstogether, prior to delivery. In an exemplary embodiment, the fibrinconstructs can be shaped to correspond to the target site by stretching,suturing, compressing, trimming and blotting one or more fibrinconstructs.

In another embodiment, the method can include delivering the fibrinconstruct with optional components that can be added either during orafter preparing the fibrin construct. The optional components caninclude at least one growth factor. The growth factor can be any thatare elaborated from platelets including vascular endothelial growthfactor (VEGF), epidermal growth factor (EGF), heparin-bindingepidermal-like growth factor (HBGF), insulin-like growth factor (IGF),platelet-derived growth factor (PDGF-αβ), transforming growth factor(TGF-β), bone morphogenic protein (BMP), and fibroblast growth factor(FGF). The optional component can also include an agent, such as afibrinolysis inhibitor, a plasmin inhibitor, aprotinin, aprilotinin,alpha-2-antiplasmin, alpha-2-macroglobulin, alpha-1-antitrypsin,epsilon-aminocaproic acid or tranexamic acid, and a plasmin activatorinhibitor.

Yet another aspect discloses a kit including a borosilicate containerfor receiving a whole blood sample. The kit can include ananti-coagulant, and a coagulation activator.

The kit can also include a blood collection apparatus, such as asyringe, for receiving a whole blood sample. The syringe can also beadaptable to or removable from the container to collect the blooddirectly into the container. In one particular embodiment, theanti-coagulant is ACD-A (anticoagulant citrate dextrose solution A).

The anti-coagulant of the kit can include, but is not limited to,heparin, EDTA, citrate, oxalate, thrombin inhibitors, or other factorinhibitors. The anti-coagulant can be in powder, liquid or lyophilizedform. The anti-coagulant can also be included at a concentrationand/amount appropriate for the volume of blood to be collected or thevolume blood that can be added to the container.

The kit can also include a coagulation activator, such as an ioniccoagulation activator. The coagulation activator can include, but is notlimited to, zeolites, hemostatic agents, calcium ions, calcium salts,Factor I, Factor II, Factor III, Factor IV, Factor V, Factor VII, FactorX, Factor XI, Factor XII, Factor XIII, thrombokinase, proaccelerin,proconvertin, antihemophilic globulin, Christmas factor, prothombinase,plasma thromboplastin antecedent, Hageman factor, adenosine diphosphate,collagen, arachidonic acid, and fibinase. In an exemplary embodiment,the coagulation activator can be calcium chloride.

The kit can further include a cross-linking agent. The cross-linkingagent can include nonlimiting examples, such as a condensing agent, aphotosensitive material, an aldehyde, such as glutaraldehyde, andcarbodiimide EDC (1-ethyl-3(3 dimethyl aminopropyl)).

BRIEF DESCRIPTION OF THE DRAWINGS

The appended drawings have been included herein so that theabove-recited features, advantages and objects will become clear and canbe understood in detail. These drawings form a part of thespecification. It is to be noted, however, that the appended drawingsillustrate exemplary embodiments and should not be considered to limitthe scope.

FIG. 1 is a schematic diagram of the fibrin construct with the fibrinlayer platelet/WBC/growth factor layer and the RBC layer;

FIG. 2 shows one embodiment of the method of preparing the fibrinconstruct;

FIG. 3 is a schematic diagram of the fibrin construct showing the growthfactor depleted and growth factor enriched surfaces;

FIG. 4A shows the removal of the blood cell cap from the fibrin layer;

FIG. 4B shows the removal of the blood cell cap from the fibrin layer;

FIG. 4C shows the blood cell cap;

FIG. 4D shows the separated blood cell cap and the fibrin layer;

FIG. 5A shows a schematic top view of a PEFC on a flat guaze pad(shadedsquare 600);

FIG. 5B shows a schematic cross-section of the PEFC on the gauze pad;

FIG. 6 shows a schematic of a fibrin construct folded in half to protectthe growth factor enriched layer;

FIG. 7 shows a schematic cross-section of a multi-layered PEFC blottedbetween two pieces of gauze;

FIG. 8 shows a schematic top view of the multi-layered PEFC suturedalong the edge;

FIG. 9 shows the slow spin (−2000 xg) method of preparing the plateletenriched fibrin construct (PEFC);

FIG. 10A illustrates the fibrin construct as being stretchable, bracketindicates original length of PEFC;

FIG. 10B illustrates the blood cell cap as being suturable;

FIG. 10C illustrates the PEFC as being trimmable;

FIG. 10D illustrates the PEFC as being blottable;

FIG. 11 shows the hard spin (−3000 xg) method of preparing the PEFC;

FIG. 12 shows the ultimate strength, or maximum stress exhibited by theconstructs;

FIG. 13 shows the elongation at break, or the amount of stress exhibitedby the constructs prior to failure;

FIG. 14 shows the compression strength, axial forces exhibited by thefibrin constructs prior to being crushed;

FIG. 15 shows Wright-Giemsa staining of sections of the PEFC at 50×,100× and 200× magification;

FIG. 16 is a graph showing the VEGF and PDGF-αβ released from the PEFCin 5 ml of medium;

FIG. 17 is a bar graph showing the VEGF and PDGF-αβ content of of PEFCwith blood cell cap removed or with blood cell cap intact;

FIG. 18A shows a schematic top view of the PEFC with a temporary guidingpin across the PEFC;

FIG. 18B shows a schematic cross-section of the PEFC with the temporaryguiding pin;

FIG. 19A shows a schematic top view of the PEFC folded with the gauze;

FIG. 19B shows a schematic cross-section of the folded PEFC with thegauze;

FIG. 20A shows a schematic top view of the folded PEFC removed from thegauze;

FIG. 20B shows a schematic cross-section of the folded PEFC;

FIG. 21A shows a schematic top view of the folded PEFC sutured along theopen edge; and

FIG. 21B shows a schematic cross-section of the folded PEFC suturedalong the open edge.

DETAILED DESCRIPTION OF THE INVENTION

Certain exemplary embodiments will now be described to provide anoverall understanding of the principles of the structure, function,manufacture, and use of the constructs and methods disclosed herein. Oneor more examples of these embodiments are illustrated in theaccompanying drawings. Those skilled in the art will understand that thedevices and methods specifically described herein and illustrated in theaccompanying drawings are non-limiting exemplary embodiments and thatthe scope of the present invention is defined solely by the claims. Thefeatures illustrated or described in connection with one exemplaryembodiment may be combined with the features of other embodiments. Suchmodifications and variations are intended to be included within thescope of the present invention.

Blood clotting assists homeostasis by minimizing blood loss. Generally,blood clotting requires vessel damage, platelet aggregation, coagulationfactors and inhibition of fibrinolysis. The coagulation factors actthrough a cascade that relates the vessel damage to formation of a bloodclot (see generally L. Stryer, Biochemistry, 3rd Ed, W.H. Freeman Co.,New York; and A. G. Gilman et al., The Pharmacological Basis ofTherapeutics, 8th Edition, McGraw Hill Inc., New York, pp. 1311-1331).

Blood is made up of liquid and solid components. Blood plasma is theliquid component of blood, in which the blood cells (solid component)are suspended. It makes up about 60% of total blood volume. It iscomposed of mostly water (90% by volume), and contains dissolvedproteins, glucose, clotting factors, mineral ions, hormones and carbondioxide.

Platelets are blood cells found in the solid component of whole blood.Platelets and blood proteins work together to stop the bleeding byinitiating blood clotting, or coagulation, and forming a clot over theinjury. Platelets exert strong procoagulant and antifibrinolytic effectsthrough the release of many growth factors, such as transforming growthfactor (TGF-β1), platelet-derived growth factor (PDGF-αβ), and vascularendothelial growth factor (VEGF).

One prevalent blood protein is fibrinogen (Factor I). As used herein theterms “unaggregated fibrin” and “fibrinogen” are used interchangeably torefer to a precursor to fibrin or in its state prior to clotting orcoagulation. Fibrinogen is a 340 KDa glycoprotein hexamer containing twosets of three different chains (α, β, and γ), linked to each other bydisulfide bonds that is synthesized by the liver. In a healthyindividual, fibrinogen or unaggregated fibrin has two principlefunctions, 1) to form bridges for platelets by binding to their surfaceproteins and 2) a precursor to fibrin.

Coagulation begins almost instantly after an injury to the blood vesselhas damaged the endothelium. During the clotting process, fibrinogen isconverted to fibrin through several steps. First, thrombin cleaves theamino-terminus of the fibrinogen alpha and beta chains to fibrinopeptideA and B, respectively. The resulting fibrin monomers polymerize end toend to form protofibrils, which in turn associate laterally to formfibrin fibers. The fibrin fibers are then capable of associating to formthe fibrin gel or clot. As used herein the terms “aggregated fibrin,”“fibrin,” and “polymerized fibrin” are used interchangeably to refer tofibrin in its state after clotting or coagulation. Fibrin can also becross linked, such as by Factor XIII, to add strength to the clot.

Due to its adhesive properties, a fibrin clot atraumatically connectstissues by forming a strong joint between the tissues and adapts unevenwound surfaces. The fibrin clot promotes the ingrowth of fibroblastswhich, in combination with efficient hemostasis and adhesion between thewound surfaces, provides for an improved healing process.

It has been discovered that dimensionally stable, fibrin constructs canbe reproducibly obtained from clotted blood and can substantiallypromote wound healing. For example, fibrin constructs are useful forlocal administration to a wound site or region. The fibrin constructscan also include components that promote wound healing, such asplatelets, growth factors, white blood cells, aggregated fibrin andgrowth factors and/or other proteins.

The Fibrin Construct

The fibrin construct described herein can include a fibrin layer 100 aplatelet/white blood cell/growth factor layer 200 and a red blood celllayer 300 as shown FIG. 1. The fibrin construct can be obtained by amethod of clotting or coagulating blood in a container and separatingthe fibrin construct from unwanted components of the blood. In oneembodiment, a method of preparing the fibrin construct can include thesteps of obtaining a blood sample from a subject, mixing the bloodsample with a calcium ion in a container, exposing the blood sample to aseparation force and harvesting the fibrin construct. FIG. 2 is a flowchart illustrating the steps of such a method.

The terms “clot,” “clotting,” “coagulation,” are used interchangeablyherein, refer to a soft, nonrigid insoluble mass formed when blood gelsor the process of forming the soft, nonrigid insoluble blood mass. Theterm “clot” can apply to the coagulated phase of blood; the soft,coherent, jelly-like mass resulting from the conversion of fibrinogen tofibrin, thereby entrapping blood cells (and offer formed elements)within the coagulated plasma.

The fibrin construct described herein can be derived from coagulatedblood. In one embodiment, the fibrin construct is obtained from a sampleof blood, whole blood, or a sample of a blood derivative such as bloodcontaining an additive or diluent, or a derivative of blood, such asplasma; white blood cells; red blood cells; platelets; plasma and whiteblood cells; plasma and platelets; plasma, red blood cells andplatelets; plasma, white blood cells and platelets; or any combinationthereof.

The blood sample can be obtained from a single donor or from multipledonors and mixed together to obtain a single blood sample. The bloodsample can further be obtained from the same subject who will receivethe fibrin construct. Thus, the blood can be autologous to therecipient. The blood sample can also be obtained from a non-autologoussubject or donor or multiple donors. Moreover, the blood sample can beobtained from a heterologous subject or donor or multiple donors. Thus,the blood sample can be obtained from one or more subjects.

The term “subject” as used herein refers to an animal, in oneembodiment, a mammal and in another embodiment, a human, who can benefitfrom the compositions and methods of the present invention. There is nolimitation on the type of animal that could benefit from the presentmethods. A subject regardless of whether a human or non-human animal maybe referred to as an individual, subject, animal, host or recipient. Themethods of the present invention have applications in human medicine,veterinary medicine as well as in general, domestic or wild animalhusbandry. In one embodiment, the candidate subject is a mammal such asa human, laboratory test animal, such as a mouse, rat, rabbit, guineapig, hamster or avian species, such as a poultry bird and veterinarymedical animal, such as dog, cat, horse, cow, sheep, etc.

Moreover, the blood sample canbe less than about 0.1 ml or about 0.1 ml,0.2 ml, 0.3 ml, 0.4 ml, 0.5 ml, 0.6 ml, 0.7 ml, 0.8 ml, 0.9 ml, 1.0 ml,1.5 ml, 2 ml, 2.5 ml, 3 ml, 3.5 ml, 4 ml, 4.5 ml, 5 ml, 5.5 ml, 6 ml,6.5 ml, 7 ml, 7.5 ml, 8 ml, 8.5 ml, 9 ml, 9.5 ml, 10 ml, 11 ml, 12 ml,13 ml, 14 ml, 15 ml, 16 ml, 17 ml, 18 ml, 19 ml, 20 ml, 21 ml, 22 ml, 23ml, 24 ml, 25 ml, 26 ml, 27 ml, 28 ml, 29 ml, 30 ml, 35 ml, 40 ml, 45ml, 50 ml, 55 ml, 60 ml, 65 ml, 70 ml, 75 ml, 80 ml, 85 ml, 90 ml, 95ml, 100 ml, 110 ml, 120 ml, 130 ml, 140 ml, 150 ml, 160 ml, 170 ml, 180ml, 190 ml, 200 ml, 225 ml, 250 ml, 275 ml, 300 ml, 325 ml, 350 ml, 375ml, 400 ml, 425 ml, 450 ml, 475 ml, 500 ml, 550 ml, 600 ml, 650 ml, 700ml, 800 ml, 900 ml, 1000 ml or more. In an exemplary embodiment, theblood sample can be in the range of about 0.5 ml to about 300 ml. Inanother exemplary embodiment, the blood sample can be in the range ofabout 1 ml to about 100 ml. In yet another exemplary embodiment, bloodsample can be in the range of about 5 ml to about 50 ml.

The blood sample can be exposed to an anti-coagulant during or aftercollection of the sample to permit ease of handling the blood.Anti-coagulants such as heparin, anticoagulant citrate dextrose solutionA (ACD-A), EDTA, citrate, oxalate, thrombin inhibitors, or other factorinhibitors can be used. The anti-coagulant can be added to the bloodcollection container prior to collection or directly after collection ofthe blood sample to prevent premature coagulation.

After obtaining the blood sample, the blood can be placed in acontainer. The container can be made of agents that do not substantiallydegrade within, permeate through, react with or otherwise experiencedeleterious effects as a result of storage; or, more particularly, as aresult of a chemical interaction with the materials used with thecontainer. Exemplary embodiments of containers can include various typesof glass, such as borosilicate glass. Borosilicate glass is a type ofglass having silica and boron oxide as the main glass-formingconstituents. The boric oxide makes the glass resistant to extremetemperatures, and also improves its resistance to chemical corrosion.Therefore, borosilicate glasses are known for having very lowcoefficients of thermal expansion and high softening point, offering ahigh level of resistance to attack from water, acids, salt solutions,organic solvents and halogens.

After placing the blood sample in a container, the blood sample can beexposed to or mixed with one or more coagulation activators or clottingfactors to induce coagulation. Examples of coagulation activators orclotting factors can include, but are not limited to, zeolites,hemostatic agents, calcium ions, calcium salts, bivalent calciums,thrombin, Factor I, Factor II, Factor III, Factor IV, Factor V, FactorVII, Factor X, Factor XI, Factor XII, Factor XIII, thrombokinase,proaccelerin, proconvertin, antihemophilic globulin, Christmas factor,prothombinase, plasma thromboplastin antecedent, Hageman factor, andfibinase. The coagulation activators or clotting factors can be added tothe blood in an appropriate amount relative to the blood sample. Forexample, the concentration of calcium chloride can vary, e.g. between 10mM to 0.5 M. In an exemplary embodiment, calcium salts, such as found incalcium chloride, can be added to the blood sample to form calcium ionsand mixed with the blood to induce coagulation of the blood sample.

The blood sample can also be exposed to one or more separation forces.The separation force can include, but is not limited to, centrifugalforces such as centrifugation. The separation force can separate theblood components according to density and size. In one embodiment, theseparation force separates the blood into a density gradient. In anotherembodiment, the separation force separates the blood into a gradient ofplasma, fibrin and blood cells. In yet another embodiment, theseparation force separates the blood into a gradient of plasma,aggregated fibrin and blood cells. The blood cells can include one ormore of red blood cells, platelets, and white blood cells. Moreover, thecentrifugation force can be a speed of at least about 200 xg, 500 xg,1000 xg, 1500 xg, 1600 xg, 1700 xg, 1800 xg, 1900 ×xg, 2000 xg, 2100 xg,2200 xg, 2300 xg, 2400 xg, 2500 xg, 2600 xg, 2700 xg, 2800 xg, 2900 xg,3000 xg or greater, or any speed in between. In an exemplary embodiment,centrifugation force can be a speed of at least about 1500 xg. Inanother exemplary embodiment, centrifugation force can be a speed of atleast about 2000 xg. In yet another exemplary embodiment, centrifugationforce can be a speed of at least about 2500 xg. In another embodiment,the separation force includes more than one centrifugations. The firstcentrifugation can be at a speed of at least 2000 xg and a secondcentrifugation can be at a speed of at least 2000 xg.

The blood sample can also be exposed to a separation force for adeterminate period of time. The determinate period of time can include,but is not limited to, the time of the centrifugation. The determinateperiod of time can be sufficient to allow separation of the bloodaccording to density and size. In one embodiment, the determinate periodof time can be sufficient to allow separation of the blood into adensity gradient. In another embodiment, the determinate period of timecan be sufficient to allow separation of the blood into a gradient ofplasma, fibrin and blood cells. In yet another embodiment, thedeterminate period of time can be sufficient to allow separation of theblood into a gradient of plasma, aggregated fibrin and blood cells.Moreover, the determinate period of time can be a time of less than 1min or at least about 1 min, 2 mins, 3 mins, 4 mins, 5 mins, 6 mins, 7mins, 8 mins, 9 mins, 10 mins, 11 mins, 12 mins, 13 mins, 14 mins, 15mins, 16 mins, 17 mins, 18 mins, 19 mins, 20 mins, 21 mins, 22 mins, 23mins, 24 mins, 25 mins, 26 mins, 27 mins, 28 mins, 29 mins, 30 mins, 31mins, 32 mins, 33 mins, 34 mins, 35 mins, 36 mins, 37 mins, 38 mins, 39mins, 40 mins, 41 mins, 42 mins, 43 mins, 44 mins, 45 mins, 46 mins, 47mins, 48 mins, 49 mins, 50 mins, 51 mins, 52 mins, 53 mins, 54 mins, 55mins, 56 mins, 57 mins, 58 mins, 59 mins, 60 mins, 65 mins, 70 mins, 75mins, 80 mins, 85 mins, 90 mins, 95 mins, 100 mins or greater, or anyamount of time in between. In an exemplary embodiment, the determinateperiod of time the blood sample can be exposed to the separation forcecan be at least about 5 mins. In another exemplary embodiment, thedeterminate period of time the blood sample is exposed to the separationforce can be at least about 10 mins. In yet another exemplaryembodiment, the determinate period of time the blood sample is exposedto the separation force can be at least about 15 mins.

After separation of the blood, the fibrin construct can be harvested.The fibrin construct, as described herein, can include multiplecomponents with distinct features. In one embodiment, the construct caninclude aggregated fibrin and blood cells. The blood cells can furtherinclude platelets, white blood cells, and/or red blood cells.

In an exemplary embodiment, the fibrin construct can be obtained bycollecting whole blood in a borosilicate glass container. The blood canbe exposed to an anti-coagulant, such as ACD-A, to prevent prematurecoagulation. A coagulation activator, such as calcium chloride, can thenbe mixed with the whole blood to induce coagulation and the blood samplemixture can be exposed to a single centrifugation. The centrifugationspeed can be in the range of about 2000 xg to 5000 xg, e.g. about 3000xg for about 15 mins. After centrifugation, the fibrin construct can beharvested and, optionally, modified, e.g. trimmed, blotted, sutured,stretched, compressed, for use.

In a particular embodiment, the fibrin construct can have one side thatincludes aggregated fibrin, which can be growth factor depleted. As usedherein, the term “growth factor depleted” refers to a material, byitself, having little or no biological activity on cells, tissues ororgans. FIG. 3 schematically illustrates the fibrin layer 100 as thegrowth factor depleted side 400 of the construct. In one embodiment, thegrowth factor depleted surface of the fibrin construct can besubstantially lacking growth factors. In another embodiment, the growthfactor depleted surface of the fibrin construct can be substantiallylacking cells. The growth factor depleted surface can also besubstantially lacking in blood cells, such as red blood cells, whiteblood cells, platelets. In one embodiment, the growth factor depletedsurface can be substantially lacking in red blood cells. In anotherembodiment, the growth factor depleted surface can include blood cells,such as white blood cells and platelets. In an exemplary embodiment, thegrowth factor depleted surface can include white blood cells.

The other side of the fibrin construct can include a growth factorenriched surface with blood cells. As used herein, the term “growthfactor enriched” refers to a material having biological activity thatcan interact with or have a biological effect on cells, tissues ororgans. The growth factor enriched surface can include concentratedblood cells. The growth factor enriched surface can include platelets,white blood cells, and/or red blood cells, where the platelets canfurther include unactivated and activated platelets. The growth factorenriched surface resides on one side of the fibrin construct and caninclude substantially all the platelets and growth factors or at leastabout 50%, 60%, 70%, 80%, 85%, 90%, 95%, 99% of the platelets and growthfactors. The growth factor enriched layer may not be integrated into thefibrin layer and may be rubbed off upon harsh handling. In oneembodiment, the growth factor enriched surface can selectively includeplatelets, and/or white blood cells, where the platelets can furtherinclude unactivated and activated platelets, and the growth factorenriched surface can be substantially lacking in red blood cells. FIG. 3further schematically illustrates the platelet/white blood cell/growthfactor layer 200 and the red blood cell layer 300 as part of the growthfactor enriched side 500 of the construct.

As described above, the fibrin construct can have a growth factorenriched surface concentrated with blood cells and an opposed growthfactor depleted surface that is substantially lacking in blood cells,such as red blood cells. The term “substantially,” as used herein, meansmore than about 50%, or more than about 75%, or more than about 85%, ormore than about 90%, or more than about 95% is removed. The phrase“substantially lacking” means that there is more than about 50% of theblood cells in the sample have been removed. In exemplary embodiments,more than about 75%, more than about 85%, more than about 90%, or morethan about 95% of the blood cells are removed.

In another embodiment, after separation and harvest of the aggregatedfibrin and blood cells, the blood cells can be substantially removedfrom the aggregated fibrin. The remaining fibrin construct can includeaggregated fibrin, which is growth factor depleted and exposed on bothsides of the construct. FIGS. 4A and 4B show the removal of the bloodcell cap, which includes the removal of platelets, white blood cells andred blood cells from the fibrin layer. By substantially removing thecell layers, the resulting fibrin layer 100 can be separated from thegrowth factor enriched surface 500 and can include the substantiallygrowth factor depleted surface 400.

Moreover, the fibrin construct can include platelets that are capable ofreleasing at least one growth factor. In one embodiment, the growthfactor enriched surface can include unactivated and/or activatedplatelets that are capable of releasing at least one growth factor. Inan exemplary embodiment, the fibrin construct can be a platelet enrichedfibrin construct. In another embodiment, the platelet enriched fibrinconstruct can include unactivated platelets. In yet another embodiment,the platelet enriched fibrin construct can include activated andunactivated platelets. In one more embodiment, the platelet enrichedfibrin construct can include platelets capable of releasing at least onegrowth factor.

The fibrin construct can also include chemicals released by the bloodcells, such as small molecules,glycoproteins, growth factors, cytokinesand chemokines. The chemicals can include, but are not limited to,bioactive lipids, bioactive amines, bioactive nucleosides/nucleotides,transforming growth factor (TGF-β1), heparin-binding epidermal-likegrowth factor (HBGF), platelet-derived growth factor (PDGF-αβ),insulin-like growth factor (IGF), bone morphogenic protein (BMP), andvascular endothelial growth factor (VEGF). In a particular embodiment,the fibrin construct can include a chemical gradient, such as a growthfactor gradient. The growth factor gradient can range from substantiallylacking in growth factors on the growth factor depleted surface togrowth factors substantially present on the growth factor enrichedsurface. The growth factors can be present in a concentration, eithertotal concentration or individual concentration, of at least about 0.01pg/μl, 0.02 pg/μl, 0.03 pg/μl, 0.04 pg/μl, 0.05 pg/μl, 0.06 pg/μl, 0.07pg/μl, 0.08 pg/μl, 0.09 pg/μl, 0.1 pg/μl, 0.2 pg/μl, 0.3 pg/μl, 0.4pg/μl, 0.5 pg/μl, 0.6 pg/μl, 0.7 pg/μl, 0.8 pg/μl, 0.9 pg/μl, 1.0 pg/μl,1.1 pg/μl, 1.2 pg/μl, 1.3 pg/μl, 1.4 pg/μl, 1.5 pg/μl, 1.6 pg/μl, 1.7pg/μl, 1.8 pg/μl, 1.9 pg/μl, 2.0 pg/μl, 2.5 pg/μl, 3.0 pg/μl, 3.5 pg/μl,4.0 pg/μl, 4.5 pg/μl, 5.0 pg/μl, 5.5 pg/μl, 6.0 pg/μl, 6.5 pg/μl, 7.0pg/μl, 7.5 pg/μl, 8.0 pg/μl, 8.5 pg/μl, 9.0 pg/μl, 9.5 pg/μl, 10.0pg/μl, 10.5 pg/μl, 11.0 pg/μl, 11.5 pg/μl, 12.0 pg/μl, 12.5 pg/μl, 13.0pg/μl, 13.5 pg/μl, 14.0 pg/μl, 14.5 pg/μl, 15.0 pg/μl, 15.5 pg/μl, 16.0pg/μl, 16.5 pg/μl, 17.0 pg/μl, 17.5 pg/μl, 18.5 pg/μl, 19.0 pg/μl, 19.5pg/μl, 20 pg/μl, 21 pg/μl, 22 pg/μl, 23 pg/μl, 24 pg/μl, 25 pg/μl, 26pg/μl, 27 pg/μl, 28 pg/μl, 29 pg/μl, 30 pg/μl, 31 pg/μl, 32 pg/μl, 33pg/μl, 34 pg/μl, 35 pg/μl, 36 pg/μl, 37 pg/μl, 38 pg/μl, 39 pg/μl, 40pg/μl, 41 pg/μl, 42 pg/μl, 43 pg/μl, 44 pg/μl, 45 pg/μl, 46 pg/μl, 47pg/μl, 48 pg/μl, 49 pg/μl, 50 pg/μl, 51 pg/μl, 52 pg/μl, 53 pg/μl, 54pg/μl, 55 pg/μl, 56 pg/μl, 57 pg/μl, 58 pg/μl, 59 pg/μl, 60 pg/μl, 61pg/μl, 62 pg/μl, 63 pg/μl, 64 pg/μl, 65 pg/μl, 66 pg/μl, 67 pg/μl, 68pg/μl, 69 pg/μl, 70 pg/μl, 71 pg/μl, 72 pg/μl, 73 pg/μl, 74 pg/μl, 75pg/μl, 76 pg/μl, 77 pg/μl, 78 pg/μl, 79 pg/μl, 80 pg/μl, 85 pg/μl, 90pg/μl, 95 pg/μl, 100 pg/μl, 105 pg/μl, 110 pg/μl, 115 pg/μl, 120 pg/μl,130 pg/μl, 140 pg/μl, 150 pg/μl, 160 pg/μl, 170 pg/μl, 180 pg/μl, 190pg/μl, 200 pg/μl, 225 pg/μl, 250 pg/μl, 275 pg/μl, 300 pg/μl, 325 pg/μl,350 pg/μl, 375 pg/μl, 400 pg/μl, 425 pg/μl, 450 pg/μl, 475 pg/μl, 0.5ng/μl, 0.6 ng/μl, 0.7 ng/μl, 0.8 ng/μl, 0.9 ng/μl, 1.0 ng/μl, 1.1 ng/μl,1.2 ng/μl, 1.3 ng/μl, 1.4 ng/μl, 1.5 ng/μl, 1.6 ng/μl, 1.7 ng/μl, 1.8ng/μl, 1.9 ng/μl, 2.0 ng/μl, 2.5 ng/μl, 3.0 ng/μl, 3.5 ng/μl, 4.0 ng/μl,4.5 ng/μl, 5.0 ng/μl, 5.5 ng/μl, 6.0 ng/μl, 6.5 ng/μl, 7.0 ng/μl, 7.5ng/μl, 8.0 ng/μl, 8.5 ng/μl, 9.0 ng/μl, 9.5 ng/μl, 10.0 ng/μl, 10.5ng/μl, 11.0 ng/μl, 11.5 ng/μl, 12.0 ng/μl, 12.5 ng/μl, 13.0 ng/μl, 13.5ng/μl, 14.0 ng/μl, 14.5 ng/μl, 15.0 ng/μl, 15.5 ng/μl, 16.0 ng/μl, 16.5ng/μl, 17.0 ng/μl, 17.5 ng/μl, 18.5 ng/μl, 19.0 ng/μl, 19.5 ng/μl, 20ng/μl, 21 ng/μl, 22 ng/μl, 23 ng/μl, 24 ng/μl, 25 ng/μl, 26 ng/μl, 27ng/μl, 28 ng/μl, 29 ng/μl, 30 ng/μl, 31 ng/μl, 32 ng/μl, 33 ng/μl, 34ng/μl, 35 ng/μl, 36 ng/μl, 37 ng/μl, 38 ng/μl, 39 ng/μl, 40 ng/μl, 41ng/μl, 42 ng/μl, 43 ng/μl, 44 ng/μl, 45 ng/μl, 46 ng/μl, 47 ng/μl, 48ng/μl, 49 ng/μl, 50 ng/μl, 51 ng/μl, 52 ng/μl, 53 ng/μl, 54 ng/μl, 55ng/μl, 56 ng/μl, 57 ng/μl, 58 ng/μl, 59 ng/μl, 60 ng/μl, 61 ng/μl, 62ng/μl, 63 ng/μl, 64 ng/μl, 65 ng/μl, 66 ng/μl, 67 ng/μl, 68 ng/μl, 69ng/μl, 70 ng/μl, 71 ng/μl, 72 ng/μl, 73 ng/μl, 74 ng/μl, 75 ng/μl, 76ng/μl, 77 ng/μl, 78 ng/μl, 79 ng/μl, 80 ng/μl, 85 ng/μl, 90 ng/μl, 95ng/μl, 100 ng/μl, 105 ng/μl, 110 ng/μl, 115 ng/μl, 120 ng/μl, 130 ng/μl,140 ng/μl, 150 ng/μl, 160 ng/μl, 170 ng/μl, 180 ng/μl, 190 ng/μl, 200ng/μl, 225 ng/μl, 250 ng/μl, 275 ng/μl, 300 ng/μl, 325 ng/μl, 350 ng/μl,375 ng/μl, 400 ng/μl, 425 ng/μl, 450 ng/μl, 475 ng/μl, 500 ng/μl, orgreater, or any concentration of growth factor in between. In anexemplary embodiment, the total concentration of growth factors can beat least about 1.0 pg/μl. In another exemplary embodiment, the totalconcentration of growth factors can be at least about 5.0 pg/μl. In yetanother exemplary embodiment, the total concentration of growth factorscan be at least about 10.0 pg/μl. In an additional exemplary embodiment,the total concentration of growth factors can be at least about 50.0pg/μl. In one embodiment, an individual concentration of a growthfactor, such as PDGF-αβ or VEGF, can be at least about 0.1 pg/μl. Inanother exemplary embodiment, the individual concentration of a growthfactor can be at least about 1.0 pg/μl. In yet another exemplaryembodiment, the individual concentration of a growth factor can be atleast about 5.0 pg/μl.

In one embodiment, one side of the growth factor enriched surface (500,see FIG. 3) of the fibrin construct can, optionally, include a slightlygrowth factor enriched region, which can be represented by the layer 200in FIG. 3. The term “slightly,” as used herein, means less than about50%, or less than about 25%, or less than about 15%, or less than about10%, or less than about 5% of the original growth factor enrichedsurface is present. The phrase “slightly” means that there is less thanabout 50% of the original growth factor enriched surface is present. Inexemplary embodiments, less than about 25%, less than about 15%, lessthan about 10%, or less than about 5% of the original growth factorenriched surface can be present. The slightly growth factor enrichedregion can include white blood cells and/or platelets found in layer 200of FIG. 3, where the platelets can further include unactivated andactivated platelets. The slightly growth factor enriched region can alsoinclude a layer with a portion of the white blood cell/platelet layer200, where a portion of the platelet/white blood cell/growth factorlayer has been removed and a portion of the platelet/white bloodcell/growth factor layer remains in the growth factor enriched surface500 of the fibrin construct. The growth factor enriched surface 500 canfurther be substantially lacking in red blood cells, or the red bloodcell layer 300 can be removed from the fibrin construct. In an exemplaryembodiment, the growth factor enriched surface 500 can include at leasta portion of the unactivated platelets in the platelet/white bloodcell/growth factor layer. In another exemplary embodiment, the fibrinconstruct can have a growth factor enriched surface 500 that issubstantially lacking in red blood cells, e.g. the red blood cells layer300 is substantially removed.

In another embodiment, the fibrin construct can include a blood cellgradient. The blood cell gradient can range from substantially lackingin blood cells on the growth factor depleted surface to blood cellssubstantially present on the growth factor enriched surface. The fibrinconstruct can, optionally, include a white blood cell gradient. Thewhite blood cell gradient can range from substantially lacking in whiteblood cells on the growth factor depleted surface to white blood cellssubstantially present on the growth factor enriched surface. The fibrinconstruct can, optionally, include a platelet gradient. The plateletgradient can range from substantially lacking in platelet on the growthfactor depleted surface to platelet substantially present on the growthfactor enriched surface.

In one aspect, the fibrin construct is dimensionally stable. The term“dimensionally stable,” as used herein, refers to a material havingrelatively constant dimensions, durability under stress, and resiliency.Moreover, the fibrin construct can be capable of being punctured, suchas for suturing, and retaining its dimensional stability. It can also befolded, layered with one or more additional fibrin constructs, andblotted, all without destroying the mechanical integrity of the fibrinconstruct.

In one embodiment, the dimensionally stable fibrin construct can have aresiliency that is defined by elongation at break strength, ultimatestrength and compression strength. The elongation at break strength ofthe fibrin construct can be greater than about 100% or at least about110%, 120%, 130%, 140%, 150%, 160%, 170%, 180%, 190%, 200%, 210%, 220%,230%, 240%, 250%, 260%, 270%, 280%, 290%, 300%, 350%, 400%, 450%, 500%,or greater or any break strength in between. In one embodiment, theelongation at break strength of the dimensionally stable fibrinconstruct is at least about 200%.

The ultimate strength of the dimensionally stable fibrin construct canbe greater than about 0.1 MPa, or at least about 0.11 MPa, 0.12 MPa,0.13 MPa, 0.14 MPa, 0.15 MPa, 0.16 MPa, 0.17 MPa, 0.18 MPa, 0.19 MPa,0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa, 0.5 MPa, orgreater or any ultimate strength in between. In one embodiment, theultimate strength of the dimensionally stable fibrin construct is atleast about 0.15 MPa.

The compression strength of the dimensionally stable fibrin constructcan be greater than about 10 kPa, or at least about 11 kPa, 12 kPa, 13kPa, 14 kPa, 15 kPa, 16 kPa, 17 kPa, 18 kPa, 19 kPa, 20 kPa, 21 kPa, 22kPa, 23 kPa, 24 kPa, 25 kPa, 26 kPa, 27 kPa, 28 kPa, 29 kPa, 30 kPa, 31kPa, 32 kPa, 33 kPa, 34 kPa, 35 kPa, 36 kPa, 37 kPa, 38 kPa, 39 kPa, 40kPa, 41 kPa, 42 kPa, 43 kPa, 44 kPa, 45 kPa, 46 kPa, 47 kPa, 48 kPa, 49kPa, 50 kPa, or greater or any compression strength in between. In oneembodiment, the compression strength of the dimensionally stable fibrinconstruct is at least about 30 kPa.

In an exemplary embodiment, the fibrin construct can have a growthfactor enriched surface and a growth factor depleted surface. The growthfactor enriched surface can be concentrated with blood cells andplatelets, where the platelets and/or blood cells can be capable ofreleasing at least one growth factor. The growth factor depleted surfacecan be substantially lacking in blood cells and platelets and includesaggregated fibrin. The fibrin construct can also be dimensionallystable, such that the fibrin construct can be sutured, stapled, trimmed,blotted, stretched and compressed, while maintaining many of itsdesirable properties relevant to wound healing.

Optional Components

The fibrin construct may comprise optional components that can be addedduring or after preparing the fibrin construct. Thus, in addition tofibrin and/or blood cells, the fibrin construct can include afibrinolysis inhibitor, a plasmin inhibitor, e.g. aprotinin,aprilotinin, alpha-2-antiplasmin, alpha-2-macroglobulin,alpha-1-antitrypsin, epsilon-aminocaproic acid or tranexamic acid, or aplasmin activator inhibitor, e.g. PAI-1 or PAI-2.

The fibrin constructs can be treated with additives or drugs prior toimplantation, e.g., to promote the formation of new tissue afterimplantation. Thus, for example, stem cells, growth factors, cytokines,extracellular matrix components, and other bioactive materials can beadded to the substrate to promote healing and formation of new tissue.Such additives can in general be selected according to the target site,tissue or organ being reconstructed or augmented, to ensure thatappropriate new tissue is formed at the target site (for examples ofsuch additives for use in promoting bone healing, see, e.g.,Kirker-Head, C. A. Vet. Surg. 24 (5): 408-19 (1995)). For example,vascular endothelial growth factor (VEGF, see, e.g., U.S. Pat. No.5,654,273 herein incorporated by reference) can be employed to promotethe formation of new vascular tissue. Growth factors and other additives(e.g., epidermal growth factor (EGF), heparin-binding epidermal-likegrowth factor (HBGF), fibroblast growth factor (FGF), stromal cellderived factor, insulin-like growth factor (IGF), transforming growthfactor (TGF-β1), platelet-derived growth factor (PDGF-αβ), macrophageinflammatory proteins 1 alpha (MIP-1 alpha), 2, 3 alpha, 3 beta, 4 and5, IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-8, IL-9, IL-10, IL-11,IL-12, IL-13, TNF-alpha, and TNF-beta, leptin, leukemia inhibitoryfactor (LIF), endostatin, thrombospondin, osteogenic protein-1, bonemorphogenetic proteins 2 and 7, osteonectin, somatomedin-like peptide,osteocalcin, interferon alpha, interferon alpha A, interferon beta,interferon gamma, interferon 1 alpha, cytokines, genes, proteins, andthe like) can be added in amounts in excess of any amount of such growthfactors (if any) which may be produced by the cells seeded on thesubstrate. Such additives are preferably provided in an amountsufficient to promote the formation of new tissue of a type appropriateto the tissue or organ, which is to be repaired or augmented (e.g., bycausing or accelerating infiltration of host cells into the graft).Other useful additives include antibacterial agents such as antibiotics.

Growth factors and regulatory factors can be added to the fibrinconstructs to enhance, alter or modulate proliferation and cellmaturation and differentiation of cells at the target site. The growthand activity of cells can be affected by a variety of growth factorssuch as growth hormone, somatomedins, colony stimulating factors,erythropoietin, epidermal growth factor, hepatic erythropoietic factor(hepatopoietin), and like. Other factors which regulate proliferationand/or differentiation include prostaglandins, interleukins, andnaturally-occurring chalones.

A “therapeutically effective amount” or “effective amount” is thatamount of an agent to achieve a pharmacological effect. The term“therapeutically effective amount” includes, for example, aprophylactically effective amount. An “effective amount” is an amounteffective to achieve a desired pharmacologic effect or therapeuticimprovement without undue adverse side effects. For example, aneffective amount refers to an amount that increases operativity, orincreases weight bearing load, or decreases pain, or increases growth inthe bone and cartilage of one or more joints, or reduces jointdistortion, pain, swelling, or stiffness. The effective amount of aagent will be selected by those skilled in the art depending on theparticular patient and the disease level. It is understood that “aneffect amount” or “a therapeutically effective amount” can vary fromsubject to subject, due to variation in metabolism of therapeutic agentsand/or prokinetic agents, age, weight, general condition of the subject,the condition being treated, the severity of the condition beingtreated, and the judgment of the prescribing physician.

The fibrin constructs can be used to deliver one or more therapeuticagents to a desired location. The fibrin constructs can be used todeliver therapeutic agents to an in vivo location, an in vitro location,or other locations. The fibrin constructs can be administered to theselocations using any method. Alternatively, the fibrin constructsincluding platelets and growth factors can be implanted in a body andused to deliver molecules produced by the platelets after implantation.

Release kinetics in some embodiments can be manipulated by cross-linkingthe fibrin constructs through any means. In some embodiments,cross-linking will alter, for example, the rate at which the fibrinconstruct degrades or the rate at which a compound is released from thefibrin construct by increasing structural rigidity and delayingsubsequent dissolution of the fibrin construct. The fibrin construct canbe formed in the presence of cross-linking agents or can be treated withcross-linking agents. Any technique for cross-linking materials may beused as known to one of ordinary skill in the art. Examples ofcross-linking agents include, but are not limited to, condensing agentssuch as aldehydes e.g., glutaraldehyde, carbodiimide EDC (1-ethyl-3(3dimethyl aminopropyl)), photosensitive materials that cross-link uponexposure to specific wavelengths of light, osmium tetroxide,carbodiimide hydrochloride, and NHS (n-hydroxysuccinimide).

The release kinetics of the fibrin constructs can also be controlled bymanipulating the physical and chemical composition of the fibrinconstructs. For example, small fibers of fibrin are more susceptible tohydrolysis than larger diameter fibers of fibrin. An agent deliveredwithin a fibrin construct composed of smaller fibers is released morequickly than when prepared within a construct composed of largerdiameter fibers.

The fibrin constructs can also be treated with a coating or permeatedwith a material to alter its mechanical properties. The coating canrefer to coating or permeating the fibrin construct with a material suchas, liquefied copolymers (poly-DL-lactide co-glycolide 50:50 80 mg/mlmethylene chloride). Coating may be performed in one layer, or multiplelayers until the desired mechanical properties are achieved.

The fibrin constructs can also be treated or seeded with various factorsand proteins to control the degradation/absorption of the composition inthe subject. For instance, if new cells may be slow growing, then it isbeneficial to maintain the construct integrity for a long enough periodof time to allow the new cells enough time to regenerate and grow. Onthe other hand, if the new cells are able to quickly reproduce and grow,then a short lived construct could be desirable. Varying theconcentration of aprotinin additives, aminocaproic acid, tranxemic acid,or similar fibrinolytic inhibitors or the degree of chemicalcross-linking in the construct could be used to precisely control thisvariable. The fibrin construct could also be seeded with varying growthfactors such as angiogenesis factor to promote a growth of blood vesselsupon implantation.

In one embodiment, the fibrin construct can be co-administered withanother component, such as an additional growth factor, via delivery inthe same construct. By “co-administered” is meant simultaneousadministration in the same formulation or in two different formulationsthat are combined into one formulation for adminstration. One ormultiple components can be co-administered with the fibrin construct.For example, the fibrin construct can further include a growth factorsuch as vascular endothelial growth factor (VEGF), epidermal growthfactor (EGF), heparin-binding epidermal-like growth factor (HBGF), andfibroblast growth factor (FGF). The fibrin construct can also includefibrinolysis inhibitor, a plasmin inhibitor, aprotinin, aprilotinin,alpha-2-antiplasmin, alpha-2-macroglobulin, alpha-1-antitrypsin,epsilon-aminocaproic acid or tranexamic acid, and a plasmin activatorinhibitor. In another embodiment, the fibrin construct can include across-linking agent, such as a condensing agent, a photosensitivematerial, an aldehyde, glutaraldehyde, and carbodiimide EDC (1-ethyl-3(3dimethyl aminopropyl).

Fibrin Construct Dimensions

The dimensions of the fibrin construct can be dependent on multiplefactors, such as the volume of the blood sample, the amount offibrinogen and/or aggregated fibrin present in the blood sample, thesize of the container, the amount of separation force used, the amountof time the blood sample is exposed to the separation force and anymodifications of the fibrin construct made during harvest, i.e. removalof blood cells or the growth factor enriched surface. Varying one ormore of the parameters can change the dimensions of the fibrinconstruct. For example, using a greater volume of blood in a narrowcontainer can yield a long, narrow fibrin construct.

The fibrin constructs can also be shaped into a structure with lengthand diameter dimensions selected to correspond to the target site in thesubject. The fibrin constructs can be folded, layered, stretched,compressed, trimmed or blotted to alter the size of the construct. Thefibrin constructs can be blotted on and/or between absorbent materials,such as gauze, 600, to remove excess plasma, serum or liquid in thefibrin construct, as shown in FIGS. 5A and 5B. Moreover, blotting thefibrin construct can also reduce the size of the fibrin construct, suchas making the construct thinner, without trimming or cutting the fibrinconstruct.

The fibrin construct can also be enlarged by joining, layering orbonding multiple constructs together using standard techniques such assuturing, heating, stapling, and gluing with biological glue, or acombination of these methods. The fibrin construct can also be joined orbonded to a target site in the subject. Joining, folding, layering orbonding one or more constructs together can also protect one or moresides of the construct. In one embodiment, the fibrin construct isfolded in half upon itself so that adjacent halves of the fibrinconstruct contact each other and form an inner portion of the foldedconstruct. Folding the fibrin construct can protect one side of thefibrin construct, such as the growth factor enriched layer or slightlygrowth factor enriched region, the platelet/WBC/growth factor layer 200and, optionally, the RBC layer 300, while the other side of the fibrinconstruct, the growth factor depleted surface, the fibrin layer 100forms an outer portion of the folded construct, as shown in FIG. 6.Furthermore, the folded construct can be joined or bonded together, suchas through suturing, heating, stapling, and gluing, along an edge of theconstruct to secure the construct in a folded condition.

In another embodiment, the fibrin construct can be a multilayeredconstruct. Two or more fibrin constructs can be joined together with oneside of one fibrin construct facing a side of the other fibrinconstruct, such as the growth factor enriched surfaces 500, e.g. theplatelet/WBC/growth factor layers 200 and, optionally, the RBC layers300 form an inner portion of the multilayered construct, as shown inFIG. 7. The other sides of the fibrin construct, such as the growthfactor depletedsurface 400 including the fibrin layers 100, can form theouter portions of the multilayered construct. The multilayered constructcan further be joined or bonded together, such as through joining withsutures 800 along an outer portion of an edge to secure the multilayeredconstruct, as shown in FIG. 8. Other configurations of the multilayeredconstruct can also be used, such as growth factor enriched surface 500to growth factor enriched surface 500, growth factor enriched surface500 to growth factor depletedsurface 400 and growth factordepletedsurface 400 to growth factor depletedsurface 400. In addition,when more than two fibrin constructs are layered together, variations inlayering can also be useful, such as growth factor enriched surface 500to growth factor enriched surface 500 to growth factor depletedsurface400, growth factor enriched surface 500 to growth factor depletedsurface400 to growth factor depletedsurface 400, growth factor depletedsurface400 to growth factor depletedsurface 400 to growth factor enrichedsurface 500 and any other possible variation obtained from layeringmultiple fibrin constructs.

In yet another embodiment, the fibrin construct can be multilayered witheach individual fibrin construct being a distinct component of themultilayer. For example, one or more of the fibrin constructs caninclude one or more additional components and/or altered growth factorenriched surfaces 500, e.g. slightly growth factor enriched region bysubstantially removing the blood cell layer 300. In this embodiment, onefibrin construct of the multilayer includes an individual layer with agrowth factor enriched surface 500 and a pharmaceutical composition,e.g. one or more drugs. The fibrin construct can be varied in theindividual layers and/or an additional component can differ in thealternating layers. In another embodiment, the orientation of the fibrinconstructs with respect to one another can be varied, e.g. the growthfactor enriched surfaces 500 can face one another or the growth factordepletedsurfaces 400 can face one another or the growth factor enrichedsurface 500 of one fibrin construct can face the growth factordepletedsurface 400 of another construct, or any variation thereof. Inanother embodiment, a fibrin constructs can be altered, oriented, orlayered with or without additional components to provide immediate ordelayed effect of the growth factor enriched surface 500 to the site ofimplantation.

Suturing can involve known techniques using absorbable synthetic suturematerial such as the biocompatible polymer is polyglactin andpolyglycolic acid, manufactured as Vicryl™ by Ethicon Co., Somerville,N.J. (See e.g., Craig P. H., Williams J. A., Davis K. W., et al.: ABiological Comparison of Polyglactin 910 and Polyglycolic Acid SyntheticAbsorbable Sutures. Surg. 141; 1010, (1975)). One or more fibrinconstructs can be joined to one another. Using sutures 800 as shown inFIG. 8, one or more fibrin constructs can be implanted in a tissue site.Other methods of joining involve using biological glues. Biologicalglues can adhere to tissues, attach them to each other, or attach themto other structures on the body in a few minutes, without using staplesor sutures. These glues are eliminated, in general after thecicatrization of the wound, by biodegradation, resorption or by simpledetachment in the form of scabs.

Tissue adhesives can also be used to join one or more constructstogether. Various technologies have been developed for the formulationof tissue adhesives. Some of them are of synthetic origin, such as theglues based on cyanoacrylates (2-butyl cyanoacrylate, 2-octylcyanoacrylate), or on synthetic polymers, and others contain biologicalmaterials such as collagen or fibrin (See e.g., U.S. Pat. Nos.5,844,016, 5,874,500; 5,744,545; 5,550,187 and 6,730,299).

Delivery

The fibrin constructs can be used to treat, repair or augment a tissueat a target site such as a wound, an injury or an incision. The terms“treat” or “treatment” refer to any treatment of a wound, lesion,abrasion, incision, or laceration, or wound healing in general or woundhealing associated with an invasive medical procedure or surgicalintervention; promoting wound healing, e.g., promoting healing of awound, lesion, abrasion, incision, or laceration, augmenting thesubject's natural wound healing process, increasing wound healing in asubject, relieving a condition caused that results in a wound, lesion,abrasion, incision, or laceration, or stopping the symptoms associatedwith a disease or disorder that inhibits or prevents wound healing.

Methods of delivering the fibrin construct to a target site in thesubject can include, but are not limited to, placement of the fibrinconstruct within or on a target site. The fibrin construct can be heldat the target site by methods such as, but not limited to, implantation,suturing and/or gluing the fibrin construct to the target site.Moreover, the fibrin construct can be delivered to the subjectepicutaneously, intradermally, subcutaneously, or surgically implantedwithin a target site. The fibrin construct can be implanted to repair,augment or replace (at least a portion of) a natural tissue of a subject(e.g., for veterinary or medical (human) applications). The term“implantable” means the fibrin construct can be inserted, embedded,grafted or otherwise chronically attached or placed on or in a patient.

The fibrin construct can be delivered to the target site and kept inplace at the target site by methods used in the art. Such methods caninclude, but are not limited to, suturing techniques using absorbablesynthetic suture material such as the biocompatible polymer ispolyglactin and polyglycolic acid, manufactured as Vicryl™ by EthiconCo., Somerville, N.J. (See e.g., Craig P. H., Williams J. A., Davis K.W., et al.: A Biological Comparison of Polyglactin 910 and PolyglycolicAcid Synthetic Absorbable Sutures. Surg. 141; 1010, (1975)), staples,joining with biological glues and/or tissue adhesives such as syntheticadhesives, glues based on cyanoacrylates (2-butyl cyanoacrylate, 2-octylcyanoacrylate), or on synthetic polymers, and others contain biologicalmaterials such as collagen or fibrin (See e.g., U.S. Pat. Nos.5,844,016, 5,874,500; 5,744,545; 5,550,187 and 6,730,299). A personskilled in the art will appreciate that various combinations of suchtechniques can be used as well.

In an exemplary embodiment, the fibrin construct can be used to treat,repair or augment a tissue at a target site, such as a wound, an injuryor an incision, by delivering at least one growth factor and/orplatelet. Additionally, the fibrin construct can be delivered to thetarget site to promote healing by delivering at least one growth factorand/or platelet to the target site. The fibrin construct can bedelivered to the subject epicutaneously, intradermally, subcutaneously,or surgically implanted within the target site.

Kits

The methods and compositions encompass kits for wound healing. The kitscan comprise a container, such as a borosilicate container, forreceiving a blood sample. The kit can further contain a blood collectionapparatus, such as a syringe, for receiving a whole blood sample. Thesyringe can further be adaptable to or removable from the container tocollect the blood directly into the container. The syringe can containbe configured to hold a predefined volume of blood. The syringes cancontain volumes from about 0.1 ml, 0.2 ml, 0.3 ml, 0.4 ml, 0.5 ml, 0.6ml, 0.7 ml, 0.8 ml, 0.9 ml, 1.0 ml, 1.5 ml, 2 ml, 2.5 ml, 3 ml, 3.5 ml,4 ml, 4.5 ml, 5 ml, 5.5 ml, 6 ml, 6.5 ml, 7 ml, 7.5 ml, 8 ml, 8.5 ml, 9ml, 9.5 ml, 10 ml or more or any derivative therein.

The kit can also contain an anti-coagulant. The anti-coagulant caninclude, but is not limited to, anticoagulant citrate dextrose solutionA (ACD-A), heparin, EDTA, citrate, oxalate, thrombin inhibitors, orother factor inhibitors. The anti-coagulant can be in powder, liquid orlyophilized form. The anti-coagulant can also be included at aconcentration and/amount appropriate for the volume of blood to becollected or the volume blood that can be added to the container. In anexemplary embodiment, the anti-coagulant can be ACD-A.

The kit can also include a coagulation activator, such as an ioniccoagulation activator. The coagulation activator can include, but is notlimited to, zeolites, hemostatic agents, calcium ions, calcium salts,Factor I, Factor II, Factor III, Factor IV, Factor V, Factor VII, FactorX, Factor XI, Factor XII, Factor XIII, thrombokinase, proaccelerin,proconvertin, antihemophilic globulin, Christmas factor, prothombinase,plasma thromboplastin antecedent, Hageman factor, and fibinase.

The kit can further include a cross-linking agent. The cross-linkingagent can include, but is not limited to, a condensing agent, aphotosensitive material, an aldehyde, glutaraldehyde, and carbodiimideEDC (1-ethyl-3(3 dimethyl aminopropyl)).

Storage

The fibrin constructs can be stored and used shortly beforeimplantation. The fibrin constructs can be stored in a dry or frozenstate. Storage conditions will depend on whether a therapeutic agent isincorporated onto or into the construct and whether the platelets aresubstantially removed. In embodiments where a therapeutic agent isincorporated, the construct can be stored at temperatures below 0° C.,under vacuum, or in a lyophilized state. Other storage conditions can beused, for example, at room temperature, in darkness, in vacuum or underreduced pressure, under inert atmospheres, at refrigerator temperature,in aqueous or other liquid solutions, or in powdered form depending onthe materials in and on the construct.

The fibrin constructs may be sterilized through conventional means knownto one of skilled in the art such as radiation, and heat. The fibrinconstructs can also be combined with bacteriostatic agents, such asthimerosal, to inhibit bacterial growth. In some embodiments, the fibrinconstructs can be treated with chemicals, solutions, or processes thatconfer stability in storage and transport.

EXPERIMENTAL DATA Example 1 Preparatin of Platelet Enriched FibrinConstruct (PEFC)

Soft Spin Preparations: Bovine blood samples of 6.8 ml were collectedand exposed to 1.2 ml of anti-coagulant, ACD-A (15% by volume in finalmixture). The blood samples were transferred to borosilicate glass tubeswith 180 μl of 1M CaCl₂ solution. The samples were inverted 10 times andcentrifuged at 2000 xg for 10 mins. During centrifugation, the bloodsample clotted and separated into distinct layers: a plasma layer(PLASMA), a fibrin plug layer (CLOT) and a blood cell layer (RBC). Theimages of FIG. 9 sequentially illustrate this procedure.

The blood cell layer can be physically removed by peeling the cap ofblood cells, as shown in FIGS. 4A and 4B, from the fibrin layer,resulting in a construct comprising platelet/white blood cells, as shownin FIG. 4C. Also, FIG. 4D illustrates the blood cell cap removed fromthe fibrin layer. Most of the red blood cells can further be removed byblotting, scraping, etc.

Double Soft Spin: Similar to the soft spin method, bovine blood sampleswere collected and exposed to anti-coagulant, ACD-A. The blood samples,6.8 ml, were transferred to borosilicate glass tubes with 180 μl of 1MCaCl₂ solution. The samples were centrifuged at 2000 xg for 10 mins andfibrin layer and blood cell layer were removed from the clot. The fibrinplug layer with intact blood cell layer was further centrifuged for asecond spin of 2000 xg for 10 mins. After centrifugation, the blood celllayer further separated from serum and shrunk in size.

The fibrin plug layer with intact blood cell layer has further beenshown to be blottable after soft spinning. Absorbent pads were placed oneither side of the construct to remove residual liquid from theconstruct and the remaining membrane demonstrated significant tactilestrength.

The dimensional stability and beneficial properties of the fibrinconstruct are evidenced by FIGS. 10A-10D, which show that the constructwas able to be stretched (FIG. 10A), sutured (FIG. 10B), compressed,trimmed (FIG. 10C) and blotted (FIG. 10D).

Fresh human blood samples were obtained from 6 donors with 15% ACD-A.The 8 ml samples were transferred to borosilicate glass tubes with 180μl of 1M CaCl₂ solution. Soft spins were performed on each blood sample.Formation of the fibrin constructs was highly reproducible. The fibrinplug height was approximately 40-55% of the height of the plasma layer.In addition, the fibrin constructs demonstrated structural stabilityover time.

Hard Spin Preparation: Bovine blood samples were collected andtransferred to borosilicate tubes, as described above. The samples werethen centrifuged at 3000 xg for 15 mins. The resulting construct had afibrin plug layer that was condensed into a thinner layer than obtainedin the soft spin preparations. The blood cell layer also separated intoa red blood cell layer with a platelet/white blood cell layer below thefibrin plug layer. See FIG. 11.

Fresh human blood samples were obtained from 6 donors with 15% ACD-A.The 8 ml samples were transferred to borosilicate glass tubes with 180μl of 1M CaCl₂ solution. The samples were hard spun at 3000 xg for 15mins. Robust fibrin plugs were obtained in all preparations.Reproducibility was also seen across all the samples. The fibrin pluglayer varied in thickness from 2.5 mm to 4.0 mm. In addition, the fibrinconstructs demonstrated dimensional and structural stability over time.

Soda-Lime Glass: To test the reproducibility in glass containers otherthan borosilicate, soda-lime glass containers were used with the softspin method. Fresh human blood samples from the same 6 donors describedabove were collected with 15% ACD-A. The 6.8 ml samples were transferredto borosilicate glass tubes with 180 μl of 1M CaCl₂ solution.. Thesamples were centrifuged at 2000 xg for 10 mins. After spinning, two ofthe six samples formed a fibrin plug layer. The other four samples didnot form distinct plasma layers or fibrin plug layers. Additionally, twoof the four samples also did not exhibit a clear interface between theblood cell layer and the plasma/fibrin layer.

To test if the unclotted samples would eventually form fibrin plugs, twoof the four remaining samples were allowed to rest an hour after softspinning. After one hour, the two samples formed a fibrin plug layer.However, the results indicate that clot formation in soda-lime glasscontainers does not appear to be reproducible among different samples.

Example 2 Physical Properties of the Platelet Enriched Fibrin Construct

Physical property tests of the fibrin constructs were conducted withconstructs prepared with bovine blood collected with ACD-A and shippedthe previous day. A total of 18 samples were produced consecutively,with the maximum of 6 samples in centrifuge at a time for 15 minutes at4500 RPM (2820 g) in capped borosilicate test tubes (with 180 μl of 1MCaCl₂ solution). Upon the completion of the spin, the test tubes wereimmediately removed and placed vertically in holders. The clots, whichwere ˜14 mm in diameter, were extracted one at a time using forceps;excess proximal protein was removed, excess fluid was initially removedwith gauze, and then the construct was trimmed to reduce thickness to ˜1mm after a moderate amount of fluids was removed. The constructs werestored in DPBS solution until all samples were prepared and the DPBSfluids were removed from the constructs with light compression withgauze before mechanical testing.

Ultimate Tensile Test: To test the ultimate failure load of theconstruct in tension.

A PEFC construct prepared according to the procedure of Example 2 wasplaced on a gauze pad and lightly covered on both sides to remove amoderate amount of fluids. After 5 minutes in the gauze pad with lightcompression, the construct was ˜14 mm in diameter and ˜1 mm inthickness, was further trimmed with parallel cuts on each side to make a4 mm wide strip. One end of the strip was placed in a stationary clampThe other loose end was placed in another clamp which could be pulledwith a force guage. The clamps were adjusted to remove any slack in thestrip between them and a minimal load reading (<0.5N) could beregistered on the digital gauge. The force gauge was cleared and set torecord peak reading. The construct was pulled very slowly to visualizethe failure of the construct through the fibrin layers. Upon failure,record peak load values were noted.

FIG. 12 shows the ultimate strength, or maximum stress that theconstructs withstood prior to failure, that was measured for theconstructs obtained from two different donors.

Elongation Tensile Test: To test the elongation to failure of theconstruct in tension.

A PEFC construct prepared according to the procedure of Example 2 wasplaced on a gauze pad and lightly covered on both sides to remove amoderate amount of fluids. After 5 minutes in the gauze pad with lightcompression, the construct ˜14 mm in diameter and ˜1 mm in thickness,was further trimmed with parallel cuts on each side to make a 4 wide mmstrip. One end of the strip was placed in a stationary clamp. The otherloose end was placed in another clamp which could be pulled with a forcegauge. The clamps were adjusted to remove any slack in the strip betweenthem and a minimal load reading (<0.5N) could be registered on thedigital gauge. The length of the free strip was measured and recorded.Next, the clamp with the force gauge was pulled until the stripruptured. The distance between the clamps was measured and recordedagain. The percent elongation was calculated from this data.

FIG. 13 shows the elongation at break, or the amount of stress that theconstructs withstood prior to failure, that was measured for theconstructs obtained from two different donors.

Compression Test: To test the resistive mechanical property of theconstruct in compression through a displacement half of the constructheight.

A PEFC construct prepared according to the procedure of Example 2 wasplaced on a gauze pad and lightly covered on both sides to remove amoderate amount of fluids. After 5 minutes in the gauze pad with lightcompression, the construct was ˜14 mm in diameter and ˜1 mm inthickness. With two solid constructs placed on top of each other, thesamples were placed on the plate directly under a force gauge'scompression rod, which could be translated using a micrometer. Themicrometer was dialed down slowly until a load was registered on theforce gauge less than <0.5N. Compared with a micrometer reading takenwithout the sample in place, the exact thickness of the sample wascalculated. The force gauge was cleared and set to record peak reading.The micrometer was dialed down slowly and consistently to compress thesample to half its initial thickness and the peak load was recorded.

FIG. 14 shows the compression strength, axial forces that the fibrinconstructs withstood prior to being crushed, that was recorded for twofibrin constructs obtained from two different donors.

Example 3 Biochemical Properties of the Platelet Enriched FibrinConstruct

Histology: Human PEFC clots were generated according to the procedure ofExample 1. Clots were gently blotted on kimwipes to remove excess fluid,cut into 3 sections and mounted in OCT compound on dry ice so that thecut edge created the plane for sectioning. Frozen cassettes were thensectioned in a cryostat ultra microtome at a thickness of approximately5 microns. Tissues were immediately fixed in 100% methanol for 5 minutesat room temperature after mounting on glass slides. Slides were rinsedin phosphate buffered saline and then subjected to Wright-Giemsastaining following a standard whole blood smear staining protocol.Photomicrographs were obtained from the same field of view at increasingmagnifications, as indicated in FIG. 15, using a Zeiss microscopeoutfitted with a digital color CCD camera.

FIG. 15 shows the stained sections of the PEFC at 50×, 100× and 200×.The upper non-stained portion is the fibrin, the middle section showsthe stained platelets and white blood cells and the bottom shows thestained red blood cells.

ELISA Assays: Human PEFC clots were generated according to Example 1.PEFC was placed in a 6-well culture plate well containing 5 ml ofserum-free RPMI1640 medium supplemented with penicillin, streptomycin,fungazone, and L-glutamine. At the 0 hr, 24 hrs, 48 hrs and 66 hrs timepoints, 300 ul of medium from each sample was removed and centrifuged at3000 xg to remove cellular material. 50 ul aliquots of the clearedmedium were frozen at −80° C. until the end of the study. All sampleswere diluted into the linear range of the ELISA assays using the baseculture medium described above. ELISA assays for human VEGF and PDGF-AB(BD Biosciences, Sparks MD) were carried out in triplicate according tothe manufacturer's instructions. Data, shown in FIG. 16, represents thetotal growth factor content in 5 ml of medium.

Growth Factor Analysis: Human PEFC were generated as described above andblotted on kimwipes to remove loosely associated red blood cells andexcess fluid. One set of clots was subjected to a blunt dissectionprocedure where the distal red layer comprising the cells/platelets richregion of the clot was removed by peeling it away from the dense fibrinmatrix using forceps. Each clot was weighed and then minced into ˜2 mmcubes using 2 opposing scalpels, and the pieces were homogenized in PBSsupplemented with 0.05% triton X-100 and a protease inhibitor cocktail(Thermo Fisher Scientific, Rockford, Ill.). Homogenates were thendiluted into the linear range of the ELISA assays using homogenizationbuffer. ELISA assays for human VEGF and PDGF-AB (BD Biosciences, SparksMD) were carried out in triplicate according to the manufacturer'sinstructions. Data shown in FIG. 17 represents the total growth factorcontent of the clot.

Example 4 Delivery of the Platelet Enriched Fibrin Construct

After preparation of the PEFC, nearly 80% of the platelets and growthfactors contained in the PEFC are concentrated in a thin layer on oneside of the fibrin disk substrate. This layer may not be integrated intothe fibrin layer and may be rubbed off upon harsh handling.

An effective way to protect the platelet/WBC/growth factor rich layer200 during delivery is to fold the construct in half such that thefibrin layer 100 is on the outside forming a protective jacket, such afolding technique is illustrated in FIG. 6, which shows a cross-section.The RBC layer 300 on the inside provides a tacky surface, so that thefolded shape of the PEFC is stable. This can easily be accomplished byfirst placing the PEFC on a gauze pad, 600, with the RBC layer 300 ontop, as shown in FIGS. 5A and FIG. 5B, and then placing a temporaryguiding pin 700 across the PEFC along the midline (see FIGS. 18A and18B. The PEFC can then be easily folded together with the gauze pad 600,as shown in FIGS. 19A and FIG. 19B. Applying light finger pressure onthe gauze lightly adheres the tacky RBC surfaces 300 together. Theresulting folded PEFC, shown in FIG. 20A and FIG. 20B, has sufficientmechanical properties and dimensional stability to allow for sutures 800to be passed therethrough, as demonstrated by FIGS. 21A and FIG. 21B.

A number of stitches may be placed separately or a single suture may beused along the edge. The suture tails may optionally be used to aiddelivery to the surgical site. Depending on the type of stitch pattern,the suture may be removed after delivery.

Alternatively, an even number of PEFCs may be generated during onecentrifugation cycle depending on the capacity of the centrifuge used.Each pair of PEFCs can be placed on top of each other, such that theplatelet/WBC/growth factor rich layers 200 are protected by the RBClayers 300 on one side and the fibrin layers 100 on the other side. Thepair of PEFCs can then be blotted between gauze pad layers 600 underlight pressure, which lightly adheres the tacky surface of the RBClayers 300 together (FIG. 7). Further, the construct can be joined withsutures 800 such as about is perimeter, as shown in FIG. 8, to create arobust construct protecting the contents during delivery.

A desirable and anticipated side benefit of folding or sandwiching thePEFCs is an increase in the time constant of the growth factor releaseprofile due to the added diffusion pathway.

One of skilled in the art will appreciate further features andadvantages of the invention based on the above-described embodiments.Accordingly, the invention is not to be limited by what has beenparticularly shown and described, except as indicated by the appendedclaims. All publications and references cited herein are expresslyincorporated herein by reference in their entirety.

What is claimed is: 1-20. (canceled)
 21. A bioimplantable construct,comprising: a fibrin construct derived from whole blood, having a growthfactor enriched surface concentrated with blood cells and plateletscapable of releasing a growth factor and a growth factor depletedsurface, the fibrin construct being dimensionally stable and suturable.22. The construct of claim 21, wherein the growth factor depletedsurface is substantially lacking in blood cells.
 23. The construct ofclaim 21, wherein the growth factor depleted surface is substantiallylacking in red blood cells.
 24. The construct of claim 21, wherein thegrowth factor depleted surface includes white blood cells.
 25. Theconstruct of claim 21, wherein the fibrin construct has a resiliencythat is defined by an elongation at break strength of at least about200%.
 26. The construct of claim 21, wherein the fibrin construct has astrength that is defined by an ultimate strength of at least about 0.15MPa.
 27. The construct of claim 21, wherein the fibrin construct has astrength that is defined by a compression strength of at least about 30kPa
 28. The construct of claim 21, wherein the fibrin construct is afolded construct that is folded upon itself so that adjacent halves ofthe growth factor enriched surface contact each other and form an innerportion of the folded construct while the growth factor depleted surfaceforms an outer portion of the folded construct.
 29. The construct ofclaim 28, wherein the folded construct is sutured along at least oneedge thereof to secure the folded construct in the folded condition. 30.The construct of claim 21, wherein the fibrin construct is in the formof a multilayered construct in which two fibrin constructs are joinedtogether with the growth factor enriched surfaces facing each other forman inner portion of the multilayered construct and the growth factordepleted surfaces form an outer portion of the multilayered construct.31. The construct of claim 30, wherein the multilayered constructincludes sutures extending between the adjacent constructs along atleast a portion of an edge thereof to secure the multilayered construct.32-51. (canceled)